The early stages of plastic deformation in stainless steel with a small grain sixe have been studied by in situ straining of a thin foil inside the electron microscope. TEM observations indite that the deformation process has a sequential character: Stuge I-activation of lattice dislocations; Stage Z-activation of triple point sources and formation of dislocation pile-ups; Stuge 3-propagation of slip across some of the grain boundaries by dislocation generation induced by stress concentration at the pile-up. The shear sttesses acting in each deformation stage have also been calculated using data based on the geometry of the pileups observed in thin foil. It is shown that the stress necemary to generate a dislocation from special grain boundary close to I: = 9 CSI misorientation is about 40 times higher than the stress necessary to emit a dislocation from a triple point. The calculated values of the shear stresses are in agreement with those registered in bulk specimens of stainless steel as well as they justify the sequence of dislocation events observed during in situ straining.